A new study says that 1 out of 10 teens has posted a nude photo of themselves online. An informal study I just crafted says that 9 out of 10 teens need to stop being such prudes.

From behind their bedroom doors, more than one out of every 10 teenagers has posted a nude or seminude picture of themselves or others online — a “digital tattoo” that could haunt them for the rest of their lives, according to a study released Monday.

Aside from the nudity, the survey found that at least a quarter of the young people polled had posted something they later regretted, made fun of others or created a false identity online.

While teens are spending more and more time on social-networking sites like Facebook and MySpace — with 22 percent saying they check their sites more than 10 times a day — they don’t seem to be aware of the long-term personal havoc they could create with a click of a button.

And their parents generally have little idea about what their children are up to, the poll found.

“We’ve got to stop kidding ourselves about this,”said James Steyer, chief economic officer and founder of San Francisco-based Common Sense Media, which commissioned the study. “There are enormous consequences from inappropriate behavior online.”

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